// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

#pragma once

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <x86intrin.h>

/*
 * These functions are used for validating utf8 string.
 * Details can be seen here: https://github.com/lemire/fastvalidate-utf-8
 */

/*
 * legal utf-8 byte sequence
 * http://www.unicode.org/versions/Unicode6.0.0/ch03.pdf - page 94
 *
 *  Code Points        1st       2s       3s       4s
 * U+0000..U+007F     00..7F
 * U+0080..U+07FF     C2..DF   80..BF
 * U+0800..U+0FFF     E0       A0..BF   80..BF
 * U+1000..U+CFFF     E1..EC   80..BF   80..BF
 * U+D000..U+D7FF     ED       80..9F   80..BF
 * U+E000..U+FFFF     EE..EF   80..BF   80..BF
 * U+10000..U+3FFFF   F0       90..BF   80..BF   80..BF
 * U+40000..U+FFFFF   F1..F3   80..BF   80..BF   80..BF
 * U+100000..U+10FFFF F4       80..8F   80..BF   80..BF
 *
 */

// all byte values must be no larger than 0xF4
static inline void checkSmallerThan0xF4(__m128i current_bytes, __m128i* has_error) {
    // unsigned, saturates to 0 below max
    *has_error = _mm_or_si128(*has_error, _mm_subs_epu8(current_bytes, _mm_set1_epi8(0xF4)));
}

static inline __m128i continuationLengths(__m128i high_nibbles) {
    return _mm_shuffle_epi8(_mm_setr_epi8(1, 1, 1, 1, 1, 1, 1, 1, // 0xxx (ASCII)
                                          0, 0, 0, 0,             // 10xx (continuation)
                                          2, 2,                   // 110x
                                          3,                      // 1110
                                          4), // 1111, next should be 0 (not checked here)
                            high_nibbles);
}

static inline __m128i carryContinuations(__m128i initial_lengths, __m128i previous_carries) {
    __m128i right1 = _mm_subs_epu8(_mm_alignr_epi8(initial_lengths, previous_carries, 16 - 1),
                                   _mm_set1_epi8(1));
    __m128i sum = _mm_add_epi8(initial_lengths, right1);

    __m128i right2 =
            _mm_subs_epu8(_mm_alignr_epi8(sum, previous_carries, 16 - 2), _mm_set1_epi8(2));
    return _mm_add_epi8(sum, right2);
}

static inline void checkContinuations(__m128i initial_lengths, __m128i carries,
                                      __m128i* has_error) {
    // overlap || underlap
    // carry > length && length > 0 || !(carry > length) && !(length > 0)
    // (carries > length) == (lengths > 0)
    __m128i overunder = _mm_cmpeq_epi8(_mm_cmpgt_epi8(carries, initial_lengths),
                                       _mm_cmpgt_epi8(initial_lengths, _mm_setzero_si128()));

    *has_error = _mm_or_si128(*has_error, overunder);
}

// when 0xED is found, next byte must be no larger than 0x9F
// when 0xF4 is found, next byte must be no larger than 0x8F
// next byte must be continuation, ie sign bit is set, so signed < is ok
static inline void checkFirstContinuationMax(__m128i current_bytes, __m128i off1_current_bytes,
                                             __m128i* has_error) {
    __m128i maskED = _mm_cmpeq_epi8(off1_current_bytes, _mm_set1_epi8(0xED));
    __m128i maskF4 = _mm_cmpeq_epi8(off1_current_bytes, _mm_set1_epi8(0xF4));

    __m128i badfollowED = _mm_and_si128(_mm_cmpgt_epi8(current_bytes, _mm_set1_epi8(0x9F)), maskED);
    __m128i badfollowF4 = _mm_and_si128(_mm_cmpgt_epi8(current_bytes, _mm_set1_epi8(0x8F)), maskF4);

    *has_error = _mm_or_si128(*has_error, _mm_or_si128(badfollowED, badfollowF4));
}

// map off1_hibits => error condition
// hibits     off1    cur
// C       => < C2 && true
// E       => < E1 && < A0
// F       => < F1 && < 90
// else      false && false
static inline void checkOverlong(__m128i current_bytes, __m128i off1_current_bytes, __m128i hibits,
                                 __m128i previous_hibits, __m128i* has_error) {
    __m128i off1_hibits = _mm_alignr_epi8(hibits, previous_hibits, 16 - 1);
    __m128i initial_mins =
            _mm_shuffle_epi8(_mm_setr_epi8(-128, -128, -128, -128, -128, -128, -128, -128, -128,
                                           -128, -128, -128, // 10xx => false
                                           0xC2, -128,       // 110x
                                           0xE1,             // 1110
                                           0xF1),
                             off1_hibits);

    __m128i initial_under = _mm_cmpgt_epi8(initial_mins, off1_current_bytes);

    __m128i second_mins =
            _mm_shuffle_epi8(_mm_setr_epi8(-128, -128, -128, -128, -128, -128, -128, -128, -128,
                                           -128, -128, -128, // 10xx => false
                                           127, 127,         // 110x => true
                                           0xA0,             // 1110
                                           0x90),
                             off1_hibits);
    __m128i second_under = _mm_cmpgt_epi8(second_mins, current_bytes);
    *has_error = _mm_or_si128(*has_error, _mm_and_si128(initial_under, second_under));
}

struct processed_utf_bytes {
    __m128i rawbytes;
    __m128i high_nibbles;
    __m128i carried_continuations;
};

static inline void count_nibbles(__m128i bytes, struct processed_utf_bytes* answer) {
    answer->rawbytes = bytes;
    answer->high_nibbles = _mm_and_si128(_mm_srli_epi16(bytes, 4), _mm_set1_epi8(0x0F));
}

// check whether the current bytes are valid UTF-8
// at the end of the function, previous gets updated
static struct processed_utf_bytes checkUTF8Bytes(__m128i current_bytes,
                                                 struct processed_utf_bytes* previous,
                                                 __m128i* has_error) {
    struct processed_utf_bytes pb;
    count_nibbles(current_bytes, &pb);

    checkSmallerThan0xF4(current_bytes, has_error);

    __m128i initial_lengths = continuationLengths(pb.high_nibbles);

    pb.carried_continuations = carryContinuations(initial_lengths, previous->carried_continuations);

    checkContinuations(initial_lengths, pb.carried_continuations, has_error);

    __m128i off1_current_bytes = _mm_alignr_epi8(pb.rawbytes, previous->rawbytes, 16 - 1);
    checkFirstContinuationMax(current_bytes, off1_current_bytes, has_error);

    checkOverlong(current_bytes, off1_current_bytes, pb.high_nibbles, previous->high_nibbles,
                  has_error);
    return pb;
}

static bool validate_utf8_fast(const char* src, size_t len) {
    size_t i = 0;
    __m128i has_error = _mm_setzero_si128();
    struct processed_utf_bytes previous = {.rawbytes = _mm_setzero_si128(),
                                           .high_nibbles = _mm_setzero_si128(),
                                           .carried_continuations = _mm_setzero_si128()};
    if (len >= 16) {
        for (; i <= len - 16; i += 16) {
            __m128i current_bytes = _mm_loadu_si128((const __m128i*)(src + i));
            previous = checkUTF8Bytes(current_bytes, &previous, &has_error);
        }
    }

    // last part
    if (i < len) {
        char buffer[16];
        memset(buffer, 0, 16);
        memcpy(buffer, src + i, len - i);
        __m128i current_bytes = _mm_loadu_si128((const __m128i*)(buffer));
        previous = checkUTF8Bytes(current_bytes, &previous, &has_error);
    } else {
        has_error = _mm_or_si128(
                _mm_cmpgt_epi8(previous.carried_continuations,
                               _mm_setr_epi8(9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 1)),
                has_error);
    }

    return _mm_testz_si128(has_error, has_error);
}

#ifdef __AVX2__

/*****************************/
static inline __m256i push_last_byte_of_a_to_b(__m256i a, __m256i b) {
    return _mm256_alignr_epi8(b, _mm256_permute2x128_si256(a, b, 0x21), 15);
}

static inline __m256i push_last_2bytes_of_a_to_b(__m256i a, __m256i b) {
    return _mm256_alignr_epi8(b, _mm256_permute2x128_si256(a, b, 0x21), 14);
}

// all byte values must be no larger than 0xF4
static inline void avxcheckSmallerThan0xF4(__m256i current_bytes, __m256i* has_error) {
    // unsigned, saturates to 0 below max
    *has_error =
            _mm256_or_si256(*has_error, _mm256_subs_epu8(current_bytes, _mm256_set1_epi8(0xF4)));
}

static inline __m256i avxcontinuationLengths(__m256i high_nibbles) {
    return _mm256_shuffle_epi8(_mm256_setr_epi8(1, 1, 1, 1, 1, 1, 1, 1, // 0xxx (ASCII)
                                                0, 0, 0, 0,             // 10xx (continuation)
                                                2, 2,                   // 110x
                                                3,                      // 1110
                                                4, // 1111, next should be 0 (not checked here)
                                                1, 1, 1, 1, 1, 1, 1, 1, // 0xxx (ASCII)
                                                0, 0, 0, 0,             // 10xx (continuation)
                                                2, 2,                   // 110x
                                                3,                      // 1110
                                                4 // 1111, next should be 0 (not checked here)
                                                ),
                               high_nibbles);
}

static inline __m256i avxcarryContinuations(__m256i initial_lengths, __m256i previous_carries) {
    __m256i right1 = _mm256_subs_epu8(push_last_byte_of_a_to_b(previous_carries, initial_lengths),
                                      _mm256_set1_epi8(1));
    __m256i sum = _mm256_add_epi8(initial_lengths, right1);

    __m256i right2 = _mm256_subs_epu8(push_last_2bytes_of_a_to_b(previous_carries, sum),
                                      _mm256_set1_epi8(2));
    return _mm256_add_epi8(sum, right2);
}

static inline void avxcheckContinuations(__m256i initial_lengths, __m256i carries,
                                         __m256i* has_error) {
    // overlap || underlap
    // carry > length && length > 0 || !(carry > length) && !(length > 0)
    // (carries > length) == (lengths > 0)
    __m256i overunder =
            _mm256_cmpeq_epi8(_mm256_cmpgt_epi8(carries, initial_lengths),
                              _mm256_cmpgt_epi8(initial_lengths, _mm256_setzero_si256()));

    *has_error = _mm256_or_si256(*has_error, overunder);
}

// when 0xED is found, next byte must be no larger than 0x9F
// when 0xF4 is found, next byte must be no larger than 0x8F
// next byte must be continuation, ie sign bit is set, so signed < is ok
static inline void avxcheckFirstContinuationMax(__m256i current_bytes, __m256i off1_current_bytes,
                                                __m256i* has_error) {
    __m256i maskED = _mm256_cmpeq_epi8(off1_current_bytes, _mm256_set1_epi8(0xED));
    __m256i maskF4 = _mm256_cmpeq_epi8(off1_current_bytes, _mm256_set1_epi8(0xF4));

    __m256i badfollowED =
            _mm256_and_si256(_mm256_cmpgt_epi8(current_bytes, _mm256_set1_epi8(0x9F)), maskED);
    __m256i badfollowF4 =
            _mm256_and_si256(_mm256_cmpgt_epi8(current_bytes, _mm256_set1_epi8(0x8F)), maskF4);

    *has_error = _mm256_or_si256(*has_error, _mm256_or_si256(badfollowED, badfollowF4));
}

// map off1_hibits => error condition
// hibits     off1    cur
// C       => < C2 && true
// E       => < E1 && < A0
// F       => < F1 && < 90
// else      false && false
static inline void avxcheckOverlong(__m256i current_bytes, __m256i off1_current_bytes,
                                    __m256i hibits, __m256i previous_hibits, __m256i* has_error) {
    __m256i off1_hibits = push_last_byte_of_a_to_b(previous_hibits, hibits);
    __m256i initial_mins =
            _mm256_shuffle_epi8(_mm256_setr_epi8(-128, -128, -128, -128, -128, -128, -128, -128,
                                                 -128, -128, -128, -128, // 10xx => false
                                                 0xC2, -128,             // 110x
                                                 0xE1,                   // 1110
                                                 0xF1, -128, -128, -128, -128, -128, -128, -128,
                                                 -128, -128, -128, -128, -128, // 10xx => false
                                                 0xC2, -128,                   // 110x
                                                 0xE1,                         // 1110
                                                 0xF1),
                                off1_hibits);

    __m256i initial_under = _mm256_cmpgt_epi8(initial_mins, off1_current_bytes);

    __m256i second_mins =
            _mm256_shuffle_epi8(_mm256_setr_epi8(-128, -128, -128, -128, -128, -128, -128, -128,
                                                 -128, -128, -128, -128, // 10xx => false
                                                 127, 127,               // 110x => true
                                                 0xA0,                   // 1110
                                                 0x90, -128, -128, -128, -128, -128, -128, -128,
                                                 -128, -128, -128, -128, -128, // 10xx => false
                                                 127, 127,                     // 110x => true
                                                 0xA0,                         // 1110
                                                 0x90),
                                off1_hibits);
    __m256i second_under = _mm256_cmpgt_epi8(second_mins, current_bytes);
    *has_error = _mm256_or_si256(*has_error, _mm256_and_si256(initial_under, second_under));
}

struct avx_processed_utf_bytes {
    __m256i rawbytes;
    __m256i high_nibbles;
    __m256i carried_continuations;
};

static inline void avx_count_nibbles(__m256i bytes, struct avx_processed_utf_bytes* answer) {
    answer->rawbytes = bytes;
    answer->high_nibbles = _mm256_and_si256(_mm256_srli_epi16(bytes, 4), _mm256_set1_epi8(0x0F));
}

#endif // __AVX2__
